The CAS Registry Mumber 82409-33-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,2,4,0 and 9 respectively; the second part has 2 digits, 3 and 3 respectively. Calculate Digit Verification of CAS Registry Number 82409-33: (7*8)+(6*2)+(5*4)+(4*0)+(3*9)+(2*3)+(1*3)=124 124 % 10 = 4 So 82409-33-4 is a valid CAS Registry Number.